This invention relates to an antenna system mounted on a vehicle, such as a car, and more specifically to an antenna system including an expansion-type antenna element capable of being expanded and contracted by remote control.
There are various antenna systems in which an expansion-type antenna element is controlled from a remote place, e.g. a driver's seat. Most of these systems, however, are so constructed that the antenna element may be expanded and contracted by means of a driving wire with the turning effort of a motor transmitted thereto. In this type of antenna system, electric power supplied to the motor needs to be automatically interrupted on completion of the expanding or contracting operation of the antenna element. As means for automatically disconnecting the power supply, there are generally used means to open a contact in a power supply line when a motor or a rotating drum for winding and rewinding the driving wire reaches a predetermined speed of revolution, by means of a cam mechanism to revolve in concert with the motor or rotating drum.
Meanwhile, in such type of antenna system, the driving wire stops immediately on completion of the expanding or contracting action of the antenna element, so it is necessary to separate a wire transfer mechanism from the motor, which would go on rotating by the force of inertia even though disconnected from the power supply, thereby preventing the winding from being burnt due to locking of the motor. Therefore, a clutch is interposed between the motor and the wire transfer mechanism so that the motor may race when the expansion or contraction of the antenna element is completed.
Thus, requiring special mechanical parts including a limit switch combining the cam mechanism and the contact and the clutch interposed between the motor and the wire transfer mechanism, the prior art antenna system is complicated in construction, difficult to manufacture, and susceptible to troubles caused by mechanical losses--i.e., it has low reliability. Owing to the clutch it includes, it should suffer substantial clutch noises produced on completion of the expanding and contracting operations of the antenna element.